Despite all of its benefits, be aware that shampoo with coal tar might make your scalp more sensitive to the sun. Tar can stay on your skin for 24 hours or longer, and your chances of sun damage go up during that time. Protect your head with a hat or stay in the shade if you're outside.
If you have blond or other light-colored hair, shampoo with coal tar could make it darker. Treatments with coal tar also can stain clothes or skin.
Some people don't like the way coal tar shampoos smell. You may want to use a regular shampoo and conditioner afterward to make your hair smell good and keep it shiny.